Apparatus for reduction of power-dependent optical loss in silicon photonic devices

ABSTRACT

Optical waveguides may include a substrate and a silicon based optical waveguide supported on the substrate. The silicon based optical waveguide may include a central ridge portion and a plurality of spaced apart wing portions connected through connecting portions. The number of wing portions may be greater than two. The central ridge portion may have a central ridge lateral width extent greater than a lateral width extent of at least one of the wing portions. Optical waveguides may include a substrate, a silicon based optical waveguide supported on the substrate, and a concentrator supported on the substrate and positioned within a lateral width extent of the silicon based optical waveguide and outside of a height extent of the silicon based optical waveguide. The optical waveguides may be included as part of an optical modulator.

FIELD

The present disclosure relates to semiconductor photonic devices and inparticular to silicon based photonic devices, such as waveguides andmodulators.

BACKGROUND

In silicon photonics, silicon used to carry light is supported on top ofa layer of silica and is known as silicon on insulator (SOI). Referringto FIG. 1, a conventional silicon waveguide 10 is shown. An insulator 12is etched to form a rib 14 of silicon which guides light (see the lightintensity plot 20 in FIG. 2). Rib 14 has a width di between a firstsidewall 16 and a second sidewall 18. As shown in FIG. 2, a largeportion of the optical mode is exposed to the etched sidewalls 16, 18 ofrib 14.

In the process of etching crystalline Si to form rib 14, danglingcovalent bonds are created at the etched sidewalls 16, 18. When thesedangling covalent bonds absorb light, they generate free carriers, whichcontribute to optical loss. The generation rate of free carriers isproportional to the optical power inside the waveguide. This leads to aquadratic dependence of total waveguide loss on optical power, and iscommonly known as power-dependent loss.

The higher the loss in a given component of a silicon photonics chip(PIC) requires higher power levels, tighter design constraints on othercomponents on the PIC, reduced bandwidth, lower PIC output, reducedreceiver sensitivity, and other effects. Therefore, a need exists toreduce the optical loss when possible to reduce these and other negativeeffects.

SUMMARY

In an exemplary embodiment of the present disclosure, an opticalwaveguide for carrying light is provided. The optical waveguidecomprising a substrate and a silicon based optical waveguide supportedon the substrate. The silicon based optical waveguide comprising: acentral ridge portion having a central ridge lateral width extentbounded by a first central ridge sidewall and a second central ridgesidewall and a central ridge height extent bounded by a central ridgebottom face and a central ridge top face; a left wing ridge portionhaving a left wing ridge lateral width extent bounded by a first leftwing sidewall and a second left wing sidewall and a left wing ridgeheight extent bounded by a left wing ridge bottom face and a left wingridge top face; a right wing ridge portion having a right wing ridgelateral width extent bounded by a first right wing sidewall and a secondright wing sidewall and a right wing ridge height extent bounded by aright wing ridge bottom face and a right wing ridge top face; a leftconnecting portion connecting the central ridge portion and the leftwing ridge portion, the left connecting portion having a left connectingportion height extent bounded by a left connecting portion bottom faceand a left connecting portion top face; a right connecting portionconnecting the central ridge portion and the right wing ridge portion,the right connecting portion having a right connecting portion heightextent bounded by a right connecting portion bottom face and a rightconnecting portion top face; a second left wing ridge portion having asecond left wing ridge lateral width extent bounded by a first secondleft wing sidewall and a second second left wing sidewall and a secondleft wing ridge height extent bounded by a second left wing ridge bottomface and a second left wing ridge top face; a second right wing ridgeportion having a second right wing ridge lateral width extent bounded bya first second right wing sidewall and a second second right wingsidewall and a second right wing ridge height extent bounded by a secondright wing ridge bottom face and a second right wing ridge top face; asecond left connecting portion connecting the left wing portion and thesecond left wing ridge portion, the second left connecting portionhaving a second left connecting portion height extent bounded by asecond left connecting portion bottom face and a second left connectingportion top face; and a second right connecting portion connecting theright wing ridge portion and the second right wing ridge portion, thesecond right connecting portion having a second right connecting portionheight extent bounded by a second right connecting portion bottom faceand a second right connecting portion top face. The central ridge heightextent and the left wing ridge height extent are both greater than theleft connecting portion height extent and the central ridge heightextent and the right wing ridge height extent are both greater than theright connecting portion height extent. The second left wing ridgeheight extent and the second left wing ridge height extent are bothgreater than the second left connecting portion height extent and theright wing ridge height extent and the second right wing ridge heightextent are both greater than the second right connecting portion heightextent.

In an example thereof, the central ridge bottom face, the left wingridge bottom face, the right wing ridge bottom face, the left connectingportion bottom face, and the right connecting portion bottom face, thesecond left wing ridge bottom face, the second right wing ridge bottomface, the second left connecting portion bottom face, and the secondright connecting portion bottom face form a planar bottom face of thesilicon based optical waveguide.

In another example thereof, the central ridge top face and the left wingridge top face are coplanar. In a variation thereof, the right wingridge top face and the left wing ridge top face are coplanar.

In a further example thereof, the right wing ridge top face and the leftwing ridge top face are coplanar.

In yet another example thereof, the left wing ridge top face and thesecond left wing ridge top face are coplanar.

In still another example thereof, the right wing ridge top face and thesecond right wing ridge top face are coplanar.

In yet a further example thereof, the second right wing ridge top faceand the second left wing ridge top face are coplanar.

In still a further example thereof, the central ridge lateral widthextent is greater than each of the left wing ridge lateral width extentand the right wing ridge lateral width extent.

In yet still another example thereof, a first separation between thecentral ridge portion and the left wing ridge portion is at least 250nm.

In a further yet still example thereof, a second separation between thecentral ridge portion and the right wing ridge portion is at least 250nm.

In another yet example thereof, a first separation between the left wingridge portion and the second left wing ridge portion is at least 100 nm.

In additional example thereof, a second separation between the rightwing ridge portion and the second right wing ridge portion is at least100 nm.

In yet a further additional example thereof, a concentrator supported onthe substrate and positioned within the central ridge lateral widthextent of the central ridge portion of the silicon based opticalwaveguide and outside of the central ridge height extent of the centralridge portion of the silicon based optical waveguide, the concentratorhaving a concentrator lateral width extent bounded by a firstconcentrator sidewall and a second concentrator sidewall and aconcentrator height extent bounded by a concentrator bottom face and aconcentrator top face. In a variation thereof, the silicon based opticalwaveguide is a first material and the concentrator is a second materialdifferent from the first material. In another variation thereof, thesecond material is silicon nitride. In a further variation thereof, theconcentrator is patterned on top of the silicon based optical waveguide.In yet a further variation thereof, the concentrator is separated fromthe silicon based optical waveguide by a spacer layer. In a stillfurther variation thereof, the first central ridge portion sidewall andthe second central ridge portion sidewall are both etched sidewalls. Inyet a still further variation thereof, a ratio of the central ridgelateral width extent of the silicon based optical waveguide to theconcentrator lateral width extent of the concentrator is greater than1:1 In an additional variation thereof, the ratio is at least 2:1.

In another exemplary embodiment of the present disclosure, an opticalwaveguide for carrying light is provided. The optical waveguidecomprising a substrate and a silicon based optical waveguide supportedon the substrate. The silicon based optical waveguide comprising acentral ridge portion having a central ridge lateral width extentbounded by a first central ridge sidewall and a second central ridgesidewall and a central ridge height extent bounded by a central ridgebottom face and a central ridge top face; a left wing ridge portionhaving a left wing ridge lateral width extent bounded by a first leftwing sidewall and a second left wing sidewall and a left wing ridgeheight extent bounded by a left wing ridge bottom face and a left wingridge top face, the central ridge lateral width extent being greaterthan the left wing ridge lateral width extent; a right wing ridgeportion having a right wing ridge lateral width extent bounded by afirst right wing sidewall and a second right wing sidewall and a rightwing ridge height extent bounded by a right wing ridge bottom face and aright wing ridge top face, the central ridge lateral width extent beinggreater than the right wing ridge lateral width extent; a leftconnecting portion connecting the central ridge portion and the leftwing ridge portion, the left connecting portion having a left connectingportion height extent bounded by a left connecting portion bottom faceand a left connecting portion top face; and a right connecting portionconnecting the central ridge portion and the right wing ridge portion,the right connecting portion having a right connecting portion heightextent bounded by a right connecting portion bottom face and a rightconnecting portion top face. The central ridge height extent and theleft wing ridge height extent are both greater than the left connectingportion height extent and the central ridge height extent and the rightwing ridge height extent are both greater than the right connectingportion height extent.

In an example thereof, the central ridge bottom face, the left wingridge bottom face, the right wing ridge bottom face, the left connectingportion bottom face, and the right connecting portion bottom face form aplanar bottom face of the silicon based optical waveguide.

In another example thereof, the central ridge top face and the left wingridge top face are coplanar. In a variation thereof, the right wingridge top face and the left wing ridge top face are coplanar.

In a further example thereof, the right wing ridge top face and the leftwing ridge top face are coplanar.

In yet another example thereof, the left wing ridge top face and thesecond left wing ridge top face are coplanar.

In still another example thereof, the right wing ridge top face and thesecond right wing ridge top face are coplanar.

In yet a further example thereof, the second right wing ridge top faceand the second left wing ridge top face are coplanar.

In still a further example thereof, the central ridge lateral widthextent is greater than each of the left wing ridge lateral width extentand the right wing ridge lateral width extent.

In yet still another example thereof, a first separation between thecentral ridge portion and the left wing ridge portion is at least 250nm.

In a further yet still example thereof, a second separation between thecentral ridge portion and the right wing ridge portion is at least 250nm.

In yet a further additional example thereof, a concentrator supported onthe substrate and positioned within the central ridge lateral widthextent of the central ridge portion of the silicon based opticalwaveguide and outside of the central ridge height extent of the centralridge portion of the silicon based optical waveguide, the concentratorhaving a concentrator lateral width extent bounded by a firstconcentrator sidewall and a second concentrator sidewall and aconcentrator height extent bounded by a concentrator bottom face and aconcentrator top face. In a variation thereof, the silicon based opticalwaveguide is a first material and the concentrator is a second materialdifferent from the first material. In another variation thereof, thesecond material is silicon nitride. In a further variation thereof, theconcentrator is patterned on top of the silicon based optical waveguide.In yet a further variation thereof, the concentrator is separated fromthe silicon based optical waveguide by a spacer layer. In a stillfurther variation thereof, the first central ridge portion sidewall andthe second central ridge portion sidewall are both etched sidewalls. Inyet a still further variation thereof, a ratio of the central ridgelateral width extent of the silicon based optical waveguide to theconcentrator lateral width extent of the concentrator is greater than1:1 In an additional variation thereof, the ratio is at least 2:1.

In a further exemplary embodiment of the present disclosure, an opticalwaveguide for carrying light is provided. The optical waveguidecomprising a substrate; a silicon based optical waveguide supported onthe substrate having a first lateral width extent bounded by a firstsidewall and a second sidewall and a first height extent bounded by afirst bottom face and a first top face, the silicon based opticalwaveguide being a first material; and a concentrator supported on thesubstrate and positioned within the first lateral width extent of thesilicon based optical waveguide and outside of the first height extentof the silicon based optical waveguide. The concentrator having a secondlateral width extent bounded by a third sidewall and a fourth sidewalland a first height extent bounded by a second bottom face and a secondtop face. The concentrator being a second material different from thefirst material.

In an example thereof, the concentrator is patterned on top of thesilicon based optical waveguide.

In another example thereof, the concentrator is separated from thesilicon based optical waveguide by a spacer layer.

In a further example thereof, the first sidewall and the second sidewallare both etched sidewalls.

In yet a further example thereof, a ratio of the first lateral widthextent of the silicon based optical waveguide to the second lateralwidth extent of the concentrator is greater than 1:1. In a variationthereof, the ratio is at least 2:1.

In still a further example thereof, the second material is siliconnitride.

In a further still exemplary embodiment of the present disclosure, anoptical modulator for use with a radio frequency driver is provided. Theoptical modulator comprising a substrate and a silicon based opticalwaveguide supported on the substrate having a first lateral width extentbounded by a first sidewall and a second sidewall and a first heightextent bounded by a first bottom face and a first top face. The siliconbased optical waveguide having a central optical guide portion being afirst material, a p-doped portion to a first side of the central opticalguide portion, and an n-doped portion to a second side of the centraloptical guide portion. The optical modulator further comprising a firstelectrical contact adapted to operatively couple the radio frequencydriver to the p-doped portion of the silicon based optical waveguide; asecond electrical contact adapted to operatively couple the radiofrequency driver to the n-doped portion of the silicon based opticalwaveguide; and a concentrator supported on the substrate and positionedwithin the first lateral width extent of the silicon based opticalwaveguide and outside of the first height extent of the silicon basedoptical waveguide. The concentrator having a second lateral width extentbounded by a third sidewall and a fourth sidewall and a first heightextent bounded by a second bottom face and a second top face, theconcentrator being a second material different from the first material.

In an example thereof, the concentrator is patterned on top of thesilicon based optical waveguide.

In another example thereof, the concentrator is separated from thesilicon based optical waveguide by a spacer layer.

In a further example thereof, the concentrator is positioned within alateral width of the central optical guide portion of the silicon basedoptical waveguide. In a variation thereof, a ratio of the lateral widthextent of the central optical guide portion of the silicon based opticalwaveguide to the second lateral width extent of the concentrator isgreater than 1:1. In another variation thereof, the second material issilicon nitride.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of thisdisclosure, and the manner of attaining them, will become more apparentand will be better understood by reference to the following descriptionof exemplary embodiments taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 illustrates a lateral cross-sectional view of a conventionalsilicon optical waveguide;

FIG. 2 illustrates a simulated lateral cross-sectional light intensityplot of light propagating along the length of the optical waveguide ofFIG. 1;

FIG. 3 illustrates a lateral cross-sectional view of a first exemplaryoptical waveguide of the present disclosure;

FIG. 4 illustrates a simulated lateral cross-sectional light intensityplot of light propagating along the length of the optical waveguide ofFIG. 3;

FIG. 5 illustrates a lateral cross-sectional view of a second exemplaryoptical waveguide of the present disclosure;

FIG. 6 illustrates a simulated lateral cross-sectional light intensityplot of light propagating along the length of the optical waveguide ofFIG. 5;

FIG. 7 illustrates a lateral cross-sectional view of a third exemplaryoptical waveguide of the present disclosure;

FIG. 8 illustrates a simulated lateral cross-sectional light intensityplot of light propagating along the length of the optical waveguide ofFIG. 7; and

FIG. 9 illustrates a lateral cross-sectional view of an exemplaryoptical modulator of the present disclosure.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates an exemplary embodiment of the invention and suchexemplification is not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE DRAWINGS

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference is now made to the embodiments illustratedin the drawings, which are described below. The embodiments disclosedherein are not intended to be exhaustive or limit the present disclosureto the precise form disclosed in the following detailed description.Rather, the embodiments are chosen and described so that others skilledin the art may utilize their teachings. Therefore, no limitation of thescope of the present disclosure is thereby intended. Correspondingreference characters indicate corresponding parts throughout the severalviews.

The terms “couples”, “coupled”, “coupler” and variations thereof areused to include both arrangements wherein the two or more components arein direct physical contact and arrangements wherein the two or morecomponents are not in direct contact with each other (e.g., thecomponents are “coupled” via at least a third component), but yet stillcooperate or interact with each other.

In some instances throughout this disclosure and in the claims, numericterminology, such as first, second, third, and fourth, is used inreference to various components or features. Such use is not intended todenote an ordering of the components or features. Rather, numericterminology is used to assist the reader in identifying the component orfeatures being referenced and should not be narrowly interpreted asproviding a specific order of components or features.

Referring to FIG. 3, a representative view of an optical waveguide 100is illustrated. FIG. 3 is a lateral cross-sectional view of opticalwaveguide 100. Optical waveguide 100 includes a substrate 102 andsilicon based optical waveguide 104 supported on substrate 102. Siliconbased optical waveguide 104 guides light (see the light intensity plot192 in FIG. 4).

In embodiments, silicon based optical waveguide 104 is made from a firstmaterial selected from any suitable semiconductor material suitable toguiding optical radiation. Exemplary materials and dopants include Si,GaAs, LiNbO3, InP, AlGaAs, electro-optic polymer. Exemplary wavelengthsof light compatible with the listed exemplary materials or otherexemplary materials include 800-980 nm, 1260-1360 nm, 1530-1565 nm, and1565-1670 nm. For the simulation shown in FIG. 4, the first material ofsilicon based optical waveguide 104 is Silicon and the surroundingmaterial of substrate 102 is Silicon dioxide.

In embodiments, silicon based optical waveguide 104 has a constantlateral cross-section along a longitudinal length of optical waveguide100. In embodiments, silicon based optical waveguide 104 has a varyinglateral cross-section along a longitudinal length of optical waveguide100. Exemplary varying lateral cross-sections include a tapered siliconbased optical waveguide 104 which changes in a linear fashion in one orboth of a vertical extent along axis 106 and a horizontal extent alongaxis 108. In examples, although the lateral cross-section of siliconbased optical waveguide 104 varies, the proportions of the features ofsilicon based optical waveguide 104 remain the same throughout thelongitudinal length of optical waveguide 100. In embodiments, siliconbased optical waveguide 104 has at least one longitudinal portion havinga constant lateral cross-section and at least one longitudinal portionhaving a varying lateral cross-section along a longitudinal length ofoptical waveguide 100.

Silicon based optical waveguide 104 includes a central ridge portion110, a left wing ridge portion 112, a right wing ridge portion 114, aleft connecting portion 116, and a right connecting portion 118. Leftconnecting portion 116 connects central ridge portion 110 and left wingridge portion 112. Right connecting portion 118 connects central ridgeportion 110 and right wing ridge portion 114. Central ridge portion 110has a central ridge lateral width extent 120 bounded by a first centralridge sidewall 122 and a second central ridge sidewall 124 and a centralridge height extent 126 bounded by a central ridge bottom face 128 and acentral ridge top face 130. Left wing ridge portion 112 has a left wingridge lateral width extent 132 bounded by a first left wing sidewall 134and a second left wing sidewall 136 and a left wing ridge height extent138 bounded by a left wing ridge bottom face 140 and a left wing ridgetop face 142. Right wing ridge portion 114 has a right wing ridgelateral width extent 144 bounded by a first right wing sidewall 146 anda second right wing sidewall 148 and a right wing ridge height extent150 bounded by a right wing ridge bottom face 152 and a right wing ridgetop face 154. Left connecting portion 116 has a left connecting portionheight extent 156 bounded by a left connecting portion bottom face 158and a left connecting portion top face 160. Right connecting portion 118has a right connecting portion height extent 162 bounded by a rightconnecting portion bottom face 164 and a right connecting portion topface 166. Central ridge height extent 126 and left wing ridge heightextent 138 are both greater than left connecting portion height extent156 and central ridge height extent 126 and right wing ridge heightextent 150 are both greater than right connecting portion height extent162.

In embodiments, silicon based optical waveguide 104 terminates at firstleft wing sidewall 134 of left wing ridge portion 112 and first rightwing sidewall 146 of right wing ridge portion 114. In the illustratedembodiment, central ridge bottom face 128, left wing ridge bottom face140, right wing ridge bottom face 152, left connecting portion bottomface 158, and right connecting portion bottom face 164 form a planarbottom face of silicon based optical waveguide 104. In embodiments, oneor more of left wing ridge bottom face 140, right wing ridge bottom face152, left connecting portion bottom face 158, and right connectingportion bottom face 164 are offset from central ridge bottom face 128.In the illustrated embodiment, central ridge top face 130 and left wingridge top face 142 are coplanar. Further, right wing ridge top face 154and left wing ridge top face 142 are coplanar.

In the illustrated embodiment of FIG. 3, silicon based optical waveguide104 includes additional wing portions, illustratively two additionalwing portions. In embodiments, further additional wing portions areprovided. In the illustrated embodiment of FIG. 3, silicon based opticalwaveguide 104 includes a second left wing ridge portion 170 having asecond left wing ridge lateral width extent 172 bounded by sidewall 174and sidewall 176 and a second left wing ridge height extent 178 boundedby a second left wing ridge bottom face 180 and a second left wing ridgetop face 182. Second left wing ridge portion 170 is connected to leftwing ridge portion 112 through a connecting portion 184 having a lateralextent 185 and a height extent 186 which is bounded by a bottom face 188and a top face 190. silicon based optical waveguide 104 further includesa second right wing ridge portion 200 having a second right wing ridgelateral width extent 202 bounded by sidewall 204 and sidewall 206 and asecond right wing ridge height extent 208 bounded by a second left wingridge bottom face 210 and a second left wing ridge top face 212. Secondright wing ridge portion 200 is connected to right wing ridge portion114 through a connecting portion 220 having a lateral extent 222 and aheight extent 224 which is bounded by a bottom face 226 and a top face228.

In the illustrated embodiment, left wing ridge height extent 138 andsecond left wing ridge height extent 178 are both greater than heightextent 186 and right wing ridge height extent 150 and second right wingridge height extent 208 are both greater than height extent 224. In theillustrated embodiment, left wing ridge top face 142 of left wing ridgeportion 112 and second left wing ridge top face 182 of second left wingridge portion 170 are coplanar. In embodiments, left wing ridge top face142 of left wing ridge portion 112 is offset relative to second leftwing ridge top face 182 of second left wing ridge portion 170. In theillustrated embodiment, right wing ridge top face 154 of right wingridge portion 114 and second left wing ridge top face 212 of secondright wing ridge portion 200 are coplanar. In embodiments, right wingridge top face 154 of right wing ridge portion 114 is offset relative tosecond left wing ridge top face 212 of second right wing ridge portion200. In the illustrated embodiment, second left wing ridge top face 182of second left wing ridge portion 170 and second left wing ridge topface 212 of second right wing ridge portion 200 are coplanar. Inembodiments, second left wing ridge top face 182 of second left wingridge portion 170 is offset relative to second left wing ridge top face212 of second right wing ridge portion 200.

In embodiments, a lateral separation between central ridge portion 110and each of left wing ridge portion 112 and right wing ridge portion 114is equal to central ridge lateral width extent 120 of central ridgeportion 110. In embodiments, a lateral separation between central ridgeportion 110 and each of left wing ridge portion 112 and right wing ridgeportion 114 is at least 250 nanometers (nm). In embodiments, a lateralseparation between each pair of left wing ridge portion 112 and secondleft wing ridge portion 170 and of right wing ridge portion 114 andsecond right wing ridge portion 200 is at least 100 nm.

Referring to FIG. 4, a simulated light intensity plot 192 for opticalwaveguide 100 is shown. As shown in light intensity plot 192, light isguided by left wing ridge portion 112 of optical waveguide 100. Thegeometry of optical waveguide 100 permits free carriers generated bysurface states of optical waveguide 100 to diffuse over a large area.For example, left wing ridge portion 112 and right wing ridge portion114 and optionally second left wing ridge portion 170 and second rightwing ridge portion 200 provide a large surface area and volume overwhich generated carriers may diffuse away from the optical mode of leftwing ridge portion 112; thereby reducing the carrier density near theoptical mode. This geometry may also lead to a greater carrierrecombination rate and a reduction in power-dependent loss.

Referring to FIG. 5, a representative view of an optical waveguide 300is illustrated. FIG. 6 is a lateral cross-sectional view of opticalwaveguide 300. optical waveguide 300 includes a substrate 302 andsilicon based optical waveguide 304 supported on substrate 302. siliconbased optical waveguide 304 guides light (see the light intensity plot392 in FIG. 4).

In embodiments, silicon based optical waveguide 304 is made from a firstmaterial selected from any suitable semiconductor material suitable toguiding optical radiation. Exemplary materials and dopants include Si,GaAs, LiNbO3, InP, AlGaAs, electro-optic polymer. Exemplary wavelengthsof light compatible with the listed exemplary materials or otherexemplary materials include 800-980 nm, 1260-1360 nm, 1530-1565 nm, and1565-1670 nm. For the simulation shown in FIG. 6, the first material ofsilicon based optical waveguide 304 is Silicon and the surroundingmaterial of substrate 302 is Silicon dioxide.

In embodiments, silicon based optical waveguide 304 has a constantlateral cross-section along a longitudinal length of optical waveguide300. In embodiments, silicon based optical waveguide 304 has a varyinglateral cross-section along a longitudinal length of optical waveguide300. Exemplary varying lateral cross-sections include a tapered siliconbased optical waveguide 304 which changes in a linear fashion in one orboth of a vertical extent along axis 106 and a horizontal extent alongaxis 108. In examples, although the lateral cross-section varies, theproportions of the features of optical waveguide 300 remain the samethroughout the longitudinal length of optical waveguide 300. Inembodiments, silicon based optical waveguide 304 has at least onelongitudinal portion having a constant lateral cross-section and atleast one longitudinal portion having a varying lateral cross-sectionalong a longitudinal length of optical waveguide 300.

Referring to FIG. 5, silicon based optical waveguide 304 a lateral widthextent 306 bounded by a first sidewall 308 and a second sidewall 310 anda height extent 312 bounded by a bottom face 314 and a top face 316. Inthe illustrated embodiment, silicon based optical waveguide 304 is notfull width, but rather has etched sidewalls 308 and 310. In embodiments,substrate 302 is full width, and sidewalls 308 and 310 correspond to theouter extent of optical waveguide 300.

Optical waveguide 300 further includes a concentrator 330 supported onsubstrate 302 and positioned within lateral width extent 306 of siliconbased optical waveguide 304 and outside of height extent 312 of siliconbased optical waveguide 304. Concentrator 330 has a lateral width extent332 bounded by a sidewall 334 and a sidewall 336 and a height extent 340bounded by a bottom face 342 and a top face 344. In embodiments, heightextent 340 is in the range of 80-100 nanometers (nm). In embodiments, aratio of lateral width extent 306 of silicon based optical waveguide 304to lateral width extent 332 of concentrator 330 is greater than 1:1. Inexamples, the ratio is at least 2:1. In embodiments, concentrator 330 ispatterned directly on top of silicon based optical waveguide 304. In theillustrated embodiment, concentrator 330 is spaced apart from siliconbased optical waveguide 304 with a spacer layer 350. In embodiments,concentrator 330 has a thickness in the range of 200-400 nm and a widthof 300-1000 nm.

Silicon based optical waveguide 304 is made of a first material whileconcentrator 330 is made of a second material, the second material beingdifferent than the first material. In the illustrated embodiment,silicon based optical waveguide 304 is made of Silicon (Si) andconcentrator 330 is made of silicon nitride (SiN). Other exemplarymaterials may be used.

Concentrator 330 assists in concentrating the optical mode of siliconbased optical waveguide 304 to the region generally directly belowconcentrator 330 as shown in light intensity plot 392. Concentrator 330does not transport the optical energy itself. By concentrating theoptical mode, the interactions with first sidewall 308 and secondsidewall 310 of silicon based optical waveguide 304 is reduced. Thislowers the free carrier generation rate and thus reduces power-dependentloss.

Referring to FIG. 7, a representative view of an optical waveguide 500is illustrated. FIG. 7 is a lateral cross-sectional view of opticalwaveguide 500. Optical waveguide 500 includes a substrate 502 andsilicon based optical waveguide 504 supported on substrate 502. siliconbased optical waveguide 504 guides light (see the light intensity plot700 in FIG. 8).

In embodiments, silicon based optical waveguide 504 is made from a firstmaterial selected from any suitable semiconductor material suitable toguiding optical radiation. Exemplary materials and dopants include Si,GaAs, LiNbO3, InP, AlGaAs, electro-optic polymer. Exemplary wavelengthsof light compatible with the listed exemplary materials or otherexemplary materials include 800-980 nm, 1260-1360 nm, 1530-1565 nm, and1565-1670 nm. For the simulation shown in FIG. 8, the first material ofsilicon based optical waveguide 504 is Silicon and the surroundingmaterial of substrate 502 is Silicon dioxide.

In embodiments, silicon based optical waveguide 504 has a constantlateral cross-section along a longitudinal length of optical waveguide500. In embodiments, silicon based optical waveguide 504 has a varyinglateral cross-section along a longitudinal length of optical waveguide500. Exemplary varying lateral cross-sections include a tapered siliconbased optical waveguide 504 which changes in a linear fashion in one orboth of a vertical extent along axis 106 and a horizontal extent alongaxis 108. In examples, although the lateral cross-section of siliconbased optical waveguide 504 varies, the proportions of the features ofsilicon based optical waveguide 504 remain the same throughout thelongitudinal length of optical waveguide 500. In embodiments, siliconbased optical waveguide 504 has at least one longitudinal portion havinga constant lateral cross-section and at least one longitudinal portionhaving a varying lateral cross-section along a longitudinal length ofoptical waveguide 500.

Silicon based optical waveguide 504 includes a central ridge portion510, a left wing ridge portion 512, a right wing ridge portion 514, aleft connecting portion 516, and a right connecting portion 518. Leftconnecting portion 516 connects central ridge portion 510 and left wingridge portion 512. Right connecting portion 518 connects central ridgeportion 510 and right wing ridge portion 514. Central ridge portion 510has a central ridge lateral width extent 520 bounded by a first centralridge sidewall 522 and a second central ridge sidewall 524 and a centralridge height extent 526 bounded by a central ridge bottom face 528 and acentral ridge top face 530. Left wing ridge portion 512 has a left wingridge lateral width extent 532 bounded by a first left wing sidewall 534and a second left wing sidewall 536 and a left wing ridge height extent538 bounded by a left wing ridge bottom face 540 and a left wing ridgetop face 542. Right wing ridge portion 514 has a right wing ridgelateral width extent 544 bounded by a first right wing sidewall 546 anda second right wing sidewall 548 and a right wing ridge height extent550 bounded by a right wing ridge bottom face 552 and a right wing ridgetop face 554. Left connecting portion 116 has a left connecting portionheight extent 556 bounded by a left connecting portion bottom face 558and a left connecting portion top face 560. Right connecting portion 518has a right connecting portion height extent 562 bounded by a rightconnecting portion bottom face 564 and a right connecting portion topface 566. Central ridge height extent 526 and left wing ridge heightextent 538 are both greater than left connecting portion height extent556 and central ridge height extent 526 and right wing ridge heightextent 550 are both greater than right connecting portion height extent562.

In embodiments, silicon based optical waveguide 504 terminates at firstleft wing sidewall 534 of left wing ridge portion 512 and first rightwing sidewall 546 of right wing ridge portion 514. In the illustratedembodiment, central ridge bottom face 528, left wing ridge bottom face540, right wing ridge bottom face 552, left connecting portion bottomface 558, and right connecting portion bottom face 564 form a planarbottom face of silicon based optical waveguide 504. In embodiments, oneor more of left wing ridge bottom face 540, right wing ridge bottom face552, left connecting portion bottom face 558, and right connectingportion bottom face 564 are offset from central ridge bottom face 528.In the illustrated embodiment, central ridge top face 530 and left wingridge top face 542 are coplanar. Further, right wing ridge top face 554and left wing ridge top face 542 are coplanar.

In the illustrated embodiment of FIG. 7, silicon based optical waveguide504 includes additional wing portions, illustratively two additionalwing portions. In embodiments, further additional wing portions areprovided. In the illustrated embodiment of FIG. 7, silicon based opticalwaveguide 504 includes a second left wing ridge portion 570 having asecond left wing ridge lateral width extent 572 bounded by sidewall 574and sidewall 576 and a second left wing ridge height extent 578 boundedby a second left wing ridge bottom face 580 and a second left wing ridgetop face 582. Second left wing ridge portion 570 is connected to leftwing ridge portion 512 through a connecting portion 584 having a lateralextent 185 and a height extent 586 which is bounded by a bottom face 588and a top face 590. Silicon based optical waveguide 504 further includesa second right wing ridge portion 600 having a second right wing ridgelateral width extent 602 bounded by sidewall 604 and sidewall 606 and asecond right wing ridge height extent 608 bounded by a second left wingridge bottom face 610 and a second left wing ridge top face 612. Secondright wing ridge portion 600 is connected to right wing ridge portion514 through a connecting portion 620 having a lateral extent 622 and aheight extent 624 which is bounded by a bottom face 626 and a top face628.

In the illustrated embodiment, left wing ridge height extent 538 andsecond left wing ridge height extent 578 are both greater than heightextent 586 and right wing ridge height extent 550 and second right wingridge height extent 608 are both greater than height extent 624. In theillustrated embodiment, left wing ridge top face 542 of left wing ridgeportion 512 and second left wing ridge top face 582 of second left wingridge portion 570 are coplanar. In embodiments, left wing ridge top face542 of left wing ridge portion 512 is offset relative to second leftwing ridge top face 582 of second left wing ridge portion 570. In theillustrated embodiment, right wing ridge top face 554 of right wingridge portion 514 and second left wing ridge top face 612 of secondright wing ridge portion 600 are coplanar. In embodiments, right wingridge top face 554 of right wing ridge portion 514 is offset relative tosecond left wing ridge top face 612 of second right wing ridge portion600. In the illustrated embodiment, second left wing ridge top face 582of second left wing ridge portion 570 and second left wing ridge topface 612 of second right wing ridge portion 600 are coplanar. Inembodiments, second left wing ridge top face 582 of second left wingridge portion 570 is offset relative to second left wing ridge top face612 of second right wing ridge portion 600.

In embodiments, a lateral separation between central ridge portion 510and each of left wing ridge portion 512 and right wing ridge portion 514is at least 250 nm. In embodiments, a lateral separation between eachpair of left wing ridge portion 512 and second left wing ridge portion570 and of right wing ridge portion 514 and second right wing ridgeportion 600 is at least 100 nm.

Optical waveguide 500 further includes a concentrator 630 supported onsubstrate 502 and positioned within central ridge lateral width extent520 of central ridge portion 510 and outside of central ridge heightextent 526 of central ridge portion 510. Concentrator 630 has a lateralwidth extent 632 bounded by a sidewall 634 and a sidewall 636 and aheight extent 640 bounded by a bottom face 642 and a top face 644. Inembodiments, height extent 640 is in the range of 80-100 nanometers(nm). In embodiments, a ratio of central ridge lateral width extent 520of central ridge portion 510 to lateral width extent 632 of concentrator630 is greater than 1:1. In examples, the ratio is at least 2:1. Inembodiments, concentrator 630 is patterned directly on top of siliconbased optical waveguide 504. In the illustrated embodiment, concentrator630 is spaced apart from central ridge portion 510 of silicon basedoptical waveguide 504 with a spacer layer 650. In embodiments,concentrator 330 has a thickness in the range of 200-400 nm and a widthof 300-1000 nm.

Silicon based optical waveguide 504 is made of a first material whileconcentrator 630 is made of a second material, the second material beingdifferent than the first material. In the illustrated embodiment,silicon based optical waveguide 504 is made of Silicon (Si) andconcentrator 630 is made of silicon nitride (SiN). Other exemplarymaterials may be used.

Concentrator 630 assists in concentrating the optical mode of siliconbased optical waveguide 504 to the region generally directly belowconcentrator 630 as shown in light intensity plot 700. Concentrator 630does not transport the optical energy itself. By concentrating theoptical mode, the interactions with first central ridge sidewall 522 andsecond central ridge sidewall 524 of central ridge portion 510 ofsilicon based optical waveguide 504 is reduced. This lowers the freecarrier generation rate and thus reduces power-dependent loss.

Referring to FIG. 8, a simulated light intensity plot 700 for opticalwaveguide 500 is shown. As shown in light intensity plot 700, light isguided by central ridge portion 510 of optical waveguide 500. Thegeometry of optical waveguide 500 permits free carriers generated bysurface states of optical waveguide 500 to diffuse over a large area.For example, left wing ridge portion 512 and right wing ridge portion514 and optionally second left wing ridge portion 570 and second rightwing ridge portion 600 provide a large surface area and volume overwhich generated carriers may diffuse away from the optical mode ofcentral ridge portion 510 of silicon based optical waveguide 504;thereby reducing the carrier density near the optical mode. Thisgeometry may also lead to a greater carrier recombination rate and areduction in power-dependent loss.

Referring to FIG. 9, an optical modulator 800 is represented. Opticalmodulator 800 includes a modified version of optical waveguide 300′including a modified silicon based optical waveguide 304′. Silicon basedoptical waveguide 304′ includes a central optical guide portion 802which carries the optical mode of optical modulator 800, a p-dopedportion 804, and a n-doped portion 806. Silicon based optical waveguide304′ has a lateral width extent 820 bounded by a first sidewall 822 anda second sidewall 824 and a height extent 830 bounded by a bottom face832 and a top face 834.

Optical waveguide 300′ further includes a first electrical contact 850adapted to operatively couple a radio frequency driver 852 to p-dopedportion 804 of the silicon based optical waveguide 304′, a secondelectrical contact 854 adapted to operatively couple radio frequencydriver 852 to n-doped portion 806 of the silicon based optical waveguide304′, and concentrator 330 supported on substrate 302 and positionedwithin lateral width extent 820 of silicon based optical waveguide 304′and outside of height extent 830 of silicon based optical waveguide304′. Concentrator 330 has a lateral width extent 332 and a heightextent 340.

Optical modulator 800 receives an electrical drive signal from radiofrequency driver 852 and light from a light source, such as a laser (notshown). Optical modulator 800 modulates the light propagating throughcentral optical guide portion 802 of silicon based optical waveguide304′ with the electrical drive signal provided by radio frequency driver852.

An advantage, among others, of the disclosed optical waveguides andmodulators is a reduction in power-dependent optical loss due to areduction in the optical mode interacting with the sidewalls of thewaveguide material. An advantage, among others, of the disclosed opticalwaveguides and modulators is that they are fully compatible withexisting silicon photonic fabrication processes. An advantage, amongothers, of the disclosed optical waveguides is that no external voltageneeds to be applied to the waveguide. An advantage, among others, of thedisclosed optical waveguides and modulators is the light remains highlyconfined in the structure. An advantage, among others, of the disclosedoptical modulators is a reduction in the series resistance of themodulator compared to designs that rely on partially etched wings toconfine the light thereby reducing the electrical power needed for theoptical modulator.

While this invention has been described as having exemplary designs, thepresent invention can be further modified within the spirit and scope ofthis disclosure. This application is therefore intended to cover anyvariations, uses, or adaptations of the invention using its generalprinciples. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

We claim:
 1. An optical waveguide for carrying light comprising: asubstrate; and a silicon based optical waveguide supported on thesubstrate, the silicon based optical waveguide comprising: a centralridge portion having a central ridge lateral width extent bounded by afirst central ridge sidewall and a second central ridge sidewall and acentral ridge height extent bounded by a central ridge bottom face and acentral ridge top face; a left wing ridge portion having a left wingridge lateral width extent bounded by a first left wing sidewall and asecond left wing sidewall and a left wing ridge height extent bounded bya left wing ridge bottom face and a left wing ridge top face; a rightwing ridge portion having a right wing ridge lateral width extentbounded by a first right wing sidewall and a second right wing sidewalland a right wing ridge height extent bounded by a right wing ridgebottom face and a right wing ridge top face; a left connecting portionconnecting the central ridge portion and the left wing ridge portion,the left connecting portion having a left connecting portion heightextent bounded by a left connecting portion bottom face and a leftconnecting portion top face; a right connecting portion connecting thecentral ridge portion and the right wing ridge portion, the rightconnecting portion having a right connecting portion height extentbounded by a right connecting portion bottom face and a right connectingportion top face; a second left wing ridge portion having a second leftwing ridge lateral width extent bounded by a first second left wingsidewall and a second second left wing sidewall and a second left wingridge height extent bounded by a second left wing ridge bottom face anda second left wing ridge top face; a second right wing ridge portionhaving a second right wing ridge lateral width extent bounded by a firstsecond right wing sidewall and a second second right wing sidewall and asecond right wing ridge height extent bounded by a second right wingridge bottom face and a second right wing ridge top face; a second leftconnecting portion connecting the left wing portion and the second leftwing ridge portion, the second left connecting portion having a secondleft connecting portion height extent bounded by a second leftconnecting portion bottom face and a second left connecting portion topface; and a second right connecting portion connecting the right wingridge portion and the second right wing ridge portion, the second rightconnecting portion having a second right connecting portion heightextent bounded by a second right connecting portion bottom face and asecond right connecting portion top face, wherein the central ridgeheight extent and the left wing ridge height extent are both greaterthan the left connecting portion height extent and the central ridgeheight extent and the right wing ridge height extent are both greaterthan the right connecting portion height extent and wherein the secondleft wing ridge height extent and the second left wing ridge heightextent are both greater than the second left connecting portion heightextent and the right wing ridge height extent and the second right wingridge height extent are both greater than the second right connectingportion height extent.
 2. The optical waveguide of claim 1, wherein thecentral ridge bottom face, the left wing ridge bottom face, the rightwing ridge bottom face, the left connecting portion bottom face, and theright connecting portion bottom face, the second left wing ridge bottomface, the second right wing ridge bottom face, the second leftconnecting portion bottom face, and the second right connecting portionbottom face form a planar bottom face of the silicon based opticalwaveguide.
 3. The optical waveguide of claim 1, wherein the centralridge top face and the left wing ridge top face are coplanar.
 4. Theoptical waveguide of claim 3, wherein the right wing ridge top face andthe left wing ridge top face are coplanar.
 5. The optical waveguide ofclaim 1, wherein the right wing ridge top face and the left wing ridgetop face are coplanar.
 6. The optical waveguide of claim 1, wherein theleft wing ridge top face and the second left wing ridge top face arecoplanar.
 7. The optical waveguide of claim 1, wherein the right wingridge top face and the second right wing ridge top face are coplanar. 8.The optical waveguide of claim 1, wherein the second right wing ridgetop face and the second left wing ridge top face are coplanar.
 9. Theoptical waveguide of claim 1, wherein the central ridge lateral widthextent is greater than each of the left wing ridge lateral width extentand the right wing ridge lateral width extent.
 10. The optical waveguideof claim 1, wherein a first separation between the central ridge portionand the left wing ridge portion is at least 250 nm.
 11. The opticalwaveguide of claim 1, wherein a second separation between the centralridge portion and the right wing ridge portion is at least 250 nm. 12.The optical waveguide of claim 1, wherein a first separation between theleft wing ridge portion and the second left wing ridge portion is atleast 100 nm.
 13. The optical waveguide of claim 1, wherein a secondseparation between the right wing ridge portion and the second rightwing ridge portion is at least 100 nm.
 14. The optical waveguide ofclaim 1, a concentrator supported on the substrate and positioned withinthe central ridge lateral width extent of the central ridge portion ofthe silicon based optical waveguide and outside of the central ridgeheight extent of the central ridge portion of the silicon based opticalwaveguide, the concentrator having a concentrator lateral width extentbounded by a first concentrator sidewall and a second concentratorsidewall and a concentrator height extent bounded by a concentratorbottom face and a concentrator top face.
 15. The optical waveguide ofclaim 14, wherein the silicon based optical waveguide is a firstmaterial and the concentrator is a second material different from thefirst material.
 16. The optical waveguide of claim 15, wherein thesecond material is silicon nitride.
 17. The optical waveguide of claim15, wherein the concentrator is patterned on top of the silicon basedoptical waveguide.
 18. The optical waveguide of claim 15, wherein theconcentrator is separated from the silicon based optical waveguide by aspacer layer.
 19. The optical waveguide of claim 14, wherein the firstcentral ridge portion sidewall and the second central ridge portionsidewall are both etched sidewalls.
 20. The optical waveguide of claim14, wherein a ratio of the central ridge lateral width extent of thesilicon based optical waveguide to the concentrator lateral width extentof the concentrator is greater than 1:1.
 21. The optical waveguide ofclaim 19, wherein the ratio is at least 2:1.
 22. An optical waveguidefor carrying light comprising: a substrate; and a silicon based opticalwaveguide supported on the substrate, the silicon based opticalwaveguide comprising: a central ridge portion having a central ridgelateral width extent bounded by a first central ridge sidewall and asecond central ridge sidewall and a central ridge height extent boundedby a central ridge bottom face and a central ridge top face; a left wingridge portion having a left wing ridge lateral width extent bounded by afirst left wing sidewall and a second left wing sidewall and a left wingridge height extent bounded by a left wing ridge bottom face and a leftwing ridge top face, the central ridge lateral width extent beinggreater than the left wing ridge lateral width extent; a right wingridge portion having a right wing ridge lateral width extent bounded bya first right wing sidewall and a second right wing sidewall and a rightwing ridge height extent bounded by a right wing ridge bottom face and aright wing ridge top face, the central ridge lateral width extent beinggreater than the right wing ridge lateral width extent; a leftconnecting portion connecting the central ridge portion and the leftwing ridge portion, the left connecting portion having a left connectingportion height extent bounded by a left connecting portion bottom faceand a left connecting portion top face; and a right connecting portionconnecting the central ridge portion and the right wing ridge portion,the right connecting portion having a right connecting portion heightextent bounded by a right connecting portion bottom face and a rightconnecting portion top face, wherein the central ridge height extent andthe left wing ridge height extent are both greater than the leftconnecting portion height extent and the central ridge height extent andthe right wing ridge height extent are both greater than the rightconnecting portion height extent.
 23. An optical waveguide for carryinglight comprising: a substrate; a silicon based optical waveguidesupported on the substrate having a first lateral width extent boundedby a first sidewall and a second sidewall and a first height extentbounded by a first bottom face and a first top face, the silicon basedoptical waveguide being a first material; and a concentrator supportedon the substrate and positioned within the first lateral width extent ofthe silicon based optical waveguide and outside of the first heightextent of the silicon based optical waveguide, the concentrator having asecond lateral width extent bounded by a third sidewall and a fourthsidewall and a first height extent bounded by a second bottom face and asecond top face, the concentrator being a second material different fromthe first material.
 24. The optical waveguide of claim 23, wherein theconcentrator is patterned on top of the silicon based optical waveguide.25. The optical waveguide of claim 23, wherein the concentrator isseparated from the silicon based optical waveguide by a spacer layer.26. The optical waveguide of claim 23, wherein the first sidewall andthe second sidewall are both etched sidewalls.
 27. The optical waveguideof claim 23, wherein a ratio of the first lateral width extent of thesilicon based optical waveguide to the second lateral width extent ofthe concentrator is greater than 1:1
 28. The optical waveguide of claim27, wherein the ratio is at least 2:1.
 29. The optical waveguide ofclaim 23, wherein the second material is silicon nitride.
 30. An opticalmodulator for use with a radio frequency driver, the optical modulatorcomprising: a substrate; a silicon based optical waveguide supported onthe substrate having a first lateral width extent bounded by a firstsidewall and a second sidewall and a first height extent bounded by afirst bottom face and a first top face, the silicon based opticalwaveguide having a central optical guide portion being a first material,a p-doped portion to a first side of the central optical guide portion,and an n-doped portion to a second side of the central optical guideportion; a first electrical contact adapted to operatively couple theradio frequency driver to the p-doped portion of the silicon basedoptical waveguide; a second electrical contact adapted to operativelycouple the radio frequency driver to the n-doped portion of the siliconbased optical waveguide; and a concentrator supported on the substrateand positioned within the first lateral width extent of the siliconbased optical waveguide and outside of the first height extent of thesilicon based optical waveguide, the concentrator having a secondlateral width extent bounded by a third sidewall and a fourth sidewalland a first height extent bounded by a second bottom face and a secondtop face, the concentrator being a second material different from thefirst material.
 31. The optical modulator of claim 30, wherein theconcentrator is patterned on top of the silicon based optical waveguide.32. The optical modulator of claim 30, wherein the concentrator isseparated from the silicon based optical waveguide by a spacer layer.33. The optical modulator of claim 30, wherein the concentrator ispositioned within a lateral width of the central optical guide portionof the silicon based optical waveguide.
 34. The optical modulator ofclaim 33, wherein a ratio of the lateral width extent of the centraloptical guide portion of the silicon based optical waveguide to thesecond lateral width extent of the concentrator is greater than 1:1 35.The optical modulator of claim 34, wherein the second material issilicon nitride.